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root/jsr166/jsr166/src/jsr166y/ForkJoinTask.java

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.1 by dl, Tue Jan 6 14:30:31 2009 UTC vs.
Revision 1.97 by jsr166, Sun Dec 30 02:05:53 2012 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8	+
9		import java.io.Serializable;
10	<	import java.util.*;
11	<	import java.util.concurrent.*;
12	<	import java.util.concurrent.atomic.*;
13	<	import sun.misc.Unsafe;
14	<	import java.lang.reflect.*;
10	>	import java.util.Collection;
11	>	import java.util.List;
12	>	import java.util.RandomAccess;
13	>	import java.lang.ref.WeakReference;
14	>	import java.lang.ref.ReferenceQueue;
15	>	import java.util.concurrent.Callable;
16	>	import java.util.concurrent.CancellationException;
17	>	import java.util.concurrent.ExecutionException;
18	>	import java.util.concurrent.Future;
19	>	import java.util.concurrent.RejectedExecutionException;
20	>	import java.util.concurrent.RunnableFuture;
21	>	import java.util.concurrent.TimeUnit;
22	>	import java.util.concurrent.TimeoutException;
23	>	import java.util.concurrent.locks.ReentrantLock;
24	>	import java.lang.reflect.Constructor;
25
26		/**
27	<	* Abstract base class for tasks that run within a ForkJoinPool.  A
28	<	* ForkJoinTask is a thread-like entity that is much lighter weight
29	<	* than a normal thread.  Huge numbers of tasks and subtasks may be
30	<	* hosted by a small number of actual threads in a ForkJoinPool,
31	<	* at the price of some usage limitations.
32	<	*
33	<	* <p> ForkJoinTasks are forms of <tt>Futures</tt> supporting a
34	<	* limited range of use.  The "lightness" of ForkJoinTasks is due to a
35	<	* set of restrictions (that are only partially statically
36	<	* enforceable) reflecting their intended use as computational tasks
37	<	* calculating pure functions or operating on purely isolated objects.
38	<	* The primary coordination mechanisms supported for ForkJoinTasks are
39	<	* <tt>fork</tt>, that arranges asynchronous execution, and
40	<	* <tt>join</tt>, that doesn't proceed until the task's result has
41	<	* been computed. (Cancellation is also supported).  The computation
42	<	* defined in the <tt>compute</tt> method should avoid
43	<	* <tt>synchronized</tt> methods or blocks, and should minimize
44	<	* blocking synchronization apart from joining other tasks or using
45	<	* synchronizers such as Phasers that are advertised to cooperate with
46	<	* fork/join scheduling. Tasks should also not perform blocking IO,
47	<	* and should ideally access variables that are completely independent
48	<	* of those accessed by other running tasks. Minor breaches of these
49	<	* restrictions, for example using shared output streams, may be
50	<	* tolerable in practice, but frequent use may result in poor
51	<	* performance, and the potential to indefinitely stall if the number
52	<	* of threads not waiting for external synchronization becomes
53	<	* exhausted. This usage restriction is in part enforced by not
54	<	* permitting checked exceptions such as IOExceptions to be
27	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
28	>	* A {@code ForkJoinTask} is a thread-like entity that is much
29	>	* lighter weight than a normal thread.  Huge numbers of tasks and
30	>	* subtasks may be hosted by a small number of actual threads in a
31	>	* ForkJoinPool, at the price of some usage limitations.
32	>	*
33	>	* <p>A "main" {@code ForkJoinTask} begins execution when it is
34	>	* explicitly submitted to a {@link ForkJoinPool}, or, if not already
35	>	* engaged in a ForkJoin computation, commenced in the {@link
36	>	* ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
37	>	* related methods.  Once started, it will usually in turn start other
38	>	* subtasks.  As indicated by the name of this class, many programs
39	>	* using {@code ForkJoinTask} employ only methods {@link #fork} and
40	>	* {@link #join}, or derivatives such as {@link
41	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
42	>	* provides a number of other methods that can come into play in
43	>	* advanced usages, as well as extension mechanics that allow support
44	>	* of new forms of fork/join processing.
45	>	*
46	>	* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
47	>	* The efficiency of {@code ForkJoinTask}s stems from a set of
48	>	* restrictions (that are only partially statically enforceable)
49	>	* reflecting their main use as computational tasks calculating pure
50	>	* functions or operating on purely isolated objects.  The primary
51	>	* coordination mechanisms are {@link #fork}, that arranges
52	>	* asynchronous execution, and {@link #join}, that doesn't proceed
53	>	* until the task's result has been computed.  Computations should
54	>	* ideally avoid {@code synchronized} methods or blocks, and should
55	>	* minimize other blocking synchronization apart from joining other
56	>	* tasks or using synchronizers such as Phasers that are advertised to
57	>	* cooperate with fork/join scheduling. Subdividable tasks should also
58	>	* not perform blocking I/O, and should ideally access variables that
59	>	* are completely independent of those accessed by other running
60	>	* tasks. These guidelines are loosely enforced by not permitting
61	>	* checked exceptions such as {@code IOExceptions} to be
62		* thrown. However, computations may still encounter unchecked
63	<	* exceptions, that are rethrown to callers attempting join
64	<	* them. These exceptions may additionally include
65	<	* RejectedExecutionExceptions stemming from internal resource
66	<	* exhaustion such as failure to allocate internal task queues.
67	<	*
68	<	* <p> The <tt>ForkJoinTask</tt> class is not usually directly
69	<	* subclassed.  Instead, you subclass one of the abstract classes that
70	<	* support different styles of fork/join processing.  Normally, a
71	<	* concrete ForkJoinTask subclass declares fields comprising its
72	<	* parameters, established in a constructor, and then defines a
73	<	* <tt>compute</tt> method that somehow uses the control methods
74	<	* supplied by this base class. While these methods have
75	<	* <tt>public</tt> access, some of them may only be called from within
76	<	* other ForkJoinTasks. Attempts to invoke them in other contexts
77	<	* result in exceptions or errors including ClassCastException.  The
78	<	* only way to invoke a "main" driver task is to submit it to a
79	<	* ForkJoinPool. Once started, this will usually in turn start other
80	<	* subtasks.
81	<	*
82	<	* <p>Most base support methods are <tt>final</tt> because their
83	<	* implementations are intrinsically tied to the underlying
84	<	* lightweight task scheduling framework, and so cannot be overridden.
85	<	* Developers creating new basic styles of fork/join processing should
86	<	* minimally implement protected methods <tt>exec</tt>,
87	<	* <tt>setRawResult</tt>, and <tt>getRawResult</tt>, while also
88	<	* introducing an abstract computational method that can be
89	<	* implemented in its subclasses. To support such extensions,
90	<	* instances of ForkJoinTasks maintain an atomically updated
91	<	* <tt>short</tt> representing user-defined control state.  Control
92	<	* state is guaranteed initially to be zero, and to be negative upon
93	<	* completion, but may otherwise be used for any other control
94	<	* purposes, such as maintaining join counts.  The {@link
95	<	* ForkJoinWorkerThread} class supports additional inspection and
96	<	* tuning methods that can be useful when developing extensions.
63	>	* exceptions, that are rethrown to callers attempting to join
64	>	* them. These exceptions may additionally include {@link
65	>	* RejectedExecutionException} stemming from internal resource
66	>	* exhaustion, such as failure to allocate internal task
67	>	* queues. Rethrown exceptions behave in the same way as regular
68	>	* exceptions, but, when possible, contain stack traces (as displayed
69	>	* for example using {@code ex.printStackTrace()}) of both the thread
70	>	* that initiated the computation as well as the thread actually
71	>	* encountering the exception; minimally only the latter.
72	>	*
73	>	* <p>It is possible to define and use ForkJoinTasks that may block,
74	>	* but doing do requires three further considerations: (1) Completion
75	>	* of few if any <em>other</em> tasks should be dependent on a task
76	>	* that blocks on external synchronization or I/O. Event-style async
77	>	* tasks that are never joined (for example, those subclassing {@link
78	>	* CountedCompleter}) often fall into this category.  (2) To minimize
79	>	* resource impact, tasks should be small; ideally performing only the
80	>	* (possibly) blocking action. (3) Unless the {@link
81	>	* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
82	>	* blocked tasks is known to be less than the pool's {@link
83	>	* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
84	>	* enough threads will be available to ensure progress or good
85	>	* performance.
86	>	*
87	>	* <p>The primary method for awaiting completion and extracting
88	>	* results of a task is {@link #join}, but there are several variants:
89	>	* The {@link Future#get} methods support interruptible and/or timed
90	>	* waits for completion and report results using {@code Future}
91	>	* conventions. Method {@link #invoke} is semantically
92	>	* equivalent to {@code fork(); join()} but always attempts to begin
93	>	* execution in the current thread. The "<em>quiet</em>" forms of
94	>	* these methods do not extract results or report exceptions. These
95	>	* may be useful when a set of tasks are being executed, and you need
96	>	* to delay processing of results or exceptions until all complete.
97	>	* Method {@code invokeAll} (available in multiple versions)
98	>	* performs the most common form of parallel invocation: forking a set
99	>	* of tasks and joining them all.
100	>	*
101	>	* <p>In the most typical usages, a fork-join pair act like a call
102	>	* (fork) and return (join) from a parallel recursive function. As is
103	>	* the case with other forms of recursive calls, returns (joins)
104	>	* should be performed innermost-first. For example, {@code a.fork();
105	>	* b.fork(); b.join(); a.join();} is likely to be substantially more
106	>	* efficient than joining {@code a} before {@code b}.
107	>	*
108	>	* <p>The execution status of tasks may be queried at several levels
109	>	* of detail: {@link #isDone} is true if a task completed in any way
110	>	* (including the case where a task was cancelled without executing);
111	>	* {@link #isCompletedNormally} is true if a task completed without
112	>	* cancellation or encountering an exception; {@link #isCancelled} is
113	>	* true if the task was cancelled (in which case {@link #getException}
114	>	* returns a {@link java.util.concurrent.CancellationException}); and
115	>	* {@link #isCompletedAbnormally} is true if a task was either
116	>	* cancelled or encountered an exception, in which case {@link
117	>	* #getException} will return either the encountered exception or
118	>	* {@link java.util.concurrent.CancellationException}.
119	>	*
120	>	* <p>The ForkJoinTask class is not usually directly subclassed.
121	>	* Instead, you subclass one of the abstract classes that support a
122	>	* particular style of fork/join processing, typically {@link
123	>	* RecursiveAction} for most computations that do not return results,
124	>	* {@link RecursiveTask} for those that do, and {@link
125	>	* CountedCompleter} for those in which completed actions trigger
126	>	* other actions.  Normally, a concrete ForkJoinTask subclass declares
127	>	* fields comprising its parameters, established in a constructor, and
128	>	* then defines a {@code compute} method that somehow uses the control
129	>	* methods supplied by this base class.
130	>	*
131	>	* <p>Method {@link #join} and its variants are appropriate for use
132	>	* only when completion dependencies are acyclic; that is, the
133	>	* parallel computation can be described as a directed acyclic graph
134	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
135	>	* tasks cyclically wait for each other.  However, this framework
136	>	* supports other methods and techniques (for example the use of
137	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
138	>	* may be of use in constructing custom subclasses for problems that
139	>	* are not statically structured as DAGs. To support such usages a
140	>	* ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
141	>	* value using {@link #setForkJoinTaskTag} or {@link
142	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
143	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
144	>	* these {@code protected} methods or tags for any purpose, but they
145	>	* may be of use in the construction of specialized subclasses.  For
146	>	* example, parallel graph traversals can use the supplied methods to
147	>	* avoid revisiting nodes/tasks that have already been processed.
148	>	* (Method names for tagging are bulky in part to encourage definition
149	>	* of methods that reflect their usage patterns.)
150	>	*
151	>	* <p>Most base support methods are {@code final}, to prevent
152	>	* overriding of implementations that are intrinsically tied to the
153	>	* underlying lightweight task scheduling framework.  Developers
154	>	* creating new basic styles of fork/join processing should minimally
155	>	* implement {@code protected} methods {@link #exec}, {@link
156	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
157	>	* an abstract computational method that can be implemented in its
158	>	* subclasses, possibly relying on other {@code protected} methods
159	>	* provided by this class.
160		*
161		* <p>ForkJoinTasks should perform relatively small amounts of
162	<	* computations, othewise splitting into smaller tasks. As a very
163	<	* rough rule of thumb, a task should perform more than 100 and less
164	<	* than 10000 basic computational steps. If tasks are too big, then
165	<	* parellelism cannot improve throughput. If too small, then memory
166	<	* and internal task maintenance overhead may overwhelm processing.
167	<	*
168	<	* <p>ForkJoinTasks are <tt>Serializable</tt>, which enables them to
169	<	* be used in extensions such as remote execution frameworks. However,
170	<	* it is in general safe to serialize tasks only before or after, but
171	<	* not during execution. Serialization is not relied on during
172	<	* execution itself.
162	>	* computation. Large tasks should be split into smaller subtasks,
163	>	* usually via recursive decomposition. As a very rough rule of thumb,
164	>	* a task should perform more than 100 and less than 10000 basic
165	>	* computational steps, and should avoid indefinite looping. If tasks
166	>	* are too big, then parallelism cannot improve throughput. If too
167	>	* small, then memory and internal task maintenance overhead may
168	>	* overwhelm processing.
169	>	*
170	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
171	>	* and {@link Callable}, that may be of use when mixing execution of
172	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
173	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
174	>	*
175	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
176	>	* used in extensions such as remote execution frameworks. It is
177	>	* sensible to serialize tasks only before or after, but not during,
178	>	* execution. Serialization is not relied on during execution itself.
179	>	*
180	>	* @since 1.7
181	>	* @author Doug Lea
182		*/
183		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
94	–	/**
95	–	* Status field holding all run status. We pack this into a single
96	–	* int both to minimize footprint overhead and to ensure atomicity
97	–	* (updates are via CAS).
98	–	*
99	–	* Status is initially zero, and takes on nonnegative values until
100	–	* completed, upon which status holds COMPLETED. CANCELLED, or
101	–	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
102	–	* blocking waits by other threads have SIGNAL_MASK bits set --
103	–	* bit 15 for external (nonFJ) waits, and the rest a count of
104	–	* waiting FJ threads.  (This representation relies on
105	–	* ForkJoinPool max thread limits). Completion of a stolen task
106	–	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
107	–	* though suboptimal for some purposes, we use basic builtin
108	–	* wait/notify to take advantage of "monitor inflation" in JVMs
109	–	* that we would otherwise need to emulate to avoid adding further
110	–	* per-task bookkeeping overhead. Note that bits 16-28 are
111	–	* currently unused. Also value 0x80000000 is available as spare
112	–	* completion value.
113	–	*/
114	–	volatile int status; // accessed directy by pool and workers
115	–
116	–	static final int COMPLETION_MASK      = 0xe0000000;
117	–	static final int NORMAL               = 0xe0000000; // == mask
118	–	static final int CANCELLED            = 0xc0000000;
119	–	static final int EXCEPTIONAL          = 0xa0000000;
120	–	static final int SIGNAL_MASK          = 0x0000ffff;
121	–	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
122	–	static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
184
185	<	/**
186	<	* Table of exceptions thrown by tasks, to enable reporting by
187	<	* callers. Because exceptions are rare, we don't directly keep
188	<	* them with task objects, but instead us a weak ref table.  Note
189	<	* that cancellation exceptions don't appear in the table, but are
190	<	* instead recorded as status values.
191	<	* Todo: Use ConcurrentReferenceHashMap
192	<	*/
193	<	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
194	<	Collections.synchronizedMap
195	<	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
196	<
197	<	// within-package utilities
185	>	/*
186	>	* See the internal documentation of class ForkJoinPool for a
187	>	* general implementation overview.  ForkJoinTasks are mainly
188	>	* responsible for maintaining their "status" field amidst relays
189	>	* to methods in ForkJoinWorkerThread and ForkJoinPool.
190	>	*
191	>	* The methods of this class are more-or-less layered into
192	>	* (1) basic status maintenance
193	>	* (2) execution and awaiting completion
194	>	* (3) user-level methods that additionally report results.
195	>	* This is sometimes hard to see because this file orders exported
196	>	* methods in a way that flows well in javadocs.
197	>	*/
198	>
199	>	/*
200	>	* The status field holds run control status bits packed into a
201	>	* single int to minimize footprint and to ensure atomicity (via
202	>	* CAS).  Status is initially zero, and takes on nonnegative
203	>	* values until completed, upon which status (anded with
204	>	* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
205	>	* undergoing blocking waits by other threads have the SIGNAL bit
206	>	* set.  Completion of a stolen task with SIGNAL set awakens any
207	>	* waiters via notifyAll. Even though suboptimal for some
208	>	* purposes, we use basic builtin wait/notify to take advantage of
209	>	* "monitor inflation" in JVMs that we would otherwise need to
210	>	* emulate to avoid adding further per-task bookkeeping overhead.
211	>	* We want these monitors to be "fat", i.e., not use biasing or
212	>	* thin-lock techniques, so use some odd coding idioms that tend
213	>	* to avoid them, mainly by arranging that every synchronized
214	>	* block performs a wait, notifyAll or both.
215	>	*
216	>	* These control bits occupy only (some of) the upper half (16
217	>	* bits) of status field. The lower bits are used for user-defined
218	>	* tags.
219	>	*/
220	>
221	>	/** The run status of this task */
222	>	volatile int status; // accessed directly by pool and workers
223	>	static final int DONE_MASK   = 0xf0000000;  // mask out non-completion bits
224	>	static final int NORMAL      = 0xf0000000;  // must be negative
225	>	static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
226	>	static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
227	>	static final int SIGNAL      = 0x00010000;  // must be >= 1 << 16
228	>	static final int SMASK       = 0x0000ffff;  // short bits for tags
229
230		/**
231	<	* Get current worker thread, or null if not a worker thread
231	>	* Marks completion and wakes up threads waiting to join this
232	>	* task.
233	>	*
234	>	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
235	>	* @return completion status on exit
236		*/
237	<	static ForkJoinWorkerThread getWorker() {
238	<	Thread t = Thread.currentThread();
239	<	return ((t instanceof ForkJoinWorkerThread)?
240	<	(ForkJoinWorkerThread)t : null);
237	>	private int setCompletion(int completion) {
238	>	for (int s;;) {
239	>	if ((s = status) < 0)
240	>	return s;
241	>	if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
242	>	if ((s >>> 16) != 0)
243	>	synchronized (this) { notifyAll(); }
244	>	return completion;
245	>	}
246	>	}
247		}
248
249		/**
250	<	* Get pool of current worker thread, or null if not a worker thread
250	>	* Primary execution method for stolen tasks. Unless done, calls
251	>	* exec and records status if completed, but doesn't wait for
252	>	* completion otherwise.
253	>	*
254	>	* @return status on exit from this method
255		*/
256	<	static ForkJoinPool getWorkerPool() {
257	<	Thread t = Thread.currentThread();
258	<	return ((t instanceof ForkJoinWorkerThread)?
259	<	((ForkJoinWorkerThread)t).pool : null);
256	>	final int doExec() {
257	>	int s; boolean completed;
258	>	if ((s = status) >= 0) {
259	>	try {
260	>	completed = exec();
261	>	} catch (Throwable rex) {
262	>	return setExceptionalCompletion(rex);
263	>	}
264	>	if (completed)
265	>	s = setCompletion(NORMAL);
266	>	}
267	>	return s;
268		}
269
270	<	final boolean casStatus(int cmp, int val) {
271	<	return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val);
270	>	/**
271	>	* Tries to set SIGNAL status unless already completed. Used by
272	>	* ForkJoinPool. Other variants are directly incorporated into
273	>	* externalAwaitDone etc.
274	>	*
275	>	* @return true if successful
276	>	*/
277	>	final boolean trySetSignal() {
278	>	int s = status;
279	>	return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL);
280		}
281
282		/**
283	<	* Workaround for not being able to rethrow unchecked exceptions.
283	>	* Blocks a non-worker-thread until completion.
284	>	* @return status upon completion
285		*/
286	<	static void rethrowException(Throwable ex) {
287	<	if (ex != null)
288	<	_unsafe.throwException(ex);
286	>	private int externalAwaitDone() {
287	>	int s;
288	>	ForkJoinPool.externalHelpJoin(this);
289	>	boolean interrupted = false;
290	>	while ((s = status) >= 0) {
291	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
292	>	synchronized (this) {
293	>	if (status >= 0) {
294	>	try {
295	>	wait();
296	>	} catch (InterruptedException ie) {
297	>	interrupted = true;
298	>	}
299	>	}
300	>	else
301	>	notifyAll();
302	>	}
303	>	}
304	>	}
305	>	if (interrupted)
306	>	Thread.currentThread().interrupt();
307	>	return s;
308		}
309
168	–	// Setting completion status
169	–
310		/**
311	<	* Mark completion and wake up threads waiting to join this task.
172	<	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
311	>	* Blocks a non-worker-thread until completion or interruption.
312		*/
313	<	final void setCompletion(int completion) {
314	<	ForkJoinPool pool = getWorkerPool();
315	<	if (pool != null) {
316	<	int s; // Clear signal bits while setting completion status
317	<	do;while ((s = status) >= 0 && !casStatus(s, completion));
318	<
319	<	if ((s & SIGNAL_MASK) != 0) {
320	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
321	<	pool.updateRunningCount(s);
322	<	synchronized(this) { notifyAll(); }
313	>	private int externalInterruptibleAwaitDone() throws InterruptedException {
314	>	int s;
315	>	if (Thread.interrupted())
316	>	throw new InterruptedException();
317	>	ForkJoinPool.externalHelpJoin(this);
318	>	while ((s = status) >= 0) {
319	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
320	>	synchronized (this) {
321	>	if (status >= 0)
322	>	wait();
323	>	else
324	>	notifyAll();
325	>	}
326		}
327		}
328	<	else
187	<	externallySetCompletion(completion);
328	>	return s;
329		}
330
331	+
332		/**
333	<	* Version of setCompletion for non-FJ threads.  Leaves signal
334	<	* bits for unblocked threads to adjust, and always notifies.
333	>	* Implementation for join, get, quietlyJoin. Directly handles
334	>	* only cases of already-completed, external wait, and
335	>	* unfork+exec.  Others are relayed to ForkJoinPool.awaitJoin.
336	>	*
337	>	* @return status upon completion
338		*/
339	<	private void externallySetCompletion(int completion) {
340	<	int s;
341	<	do;while ((s = status) >= 0 &&
342	<	!casStatus(s, (s & SIGNAL_MASK) | completion));
343	<	synchronized(this) { notifyAll(); }
339	>	private int doJoin() {
340	>	int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
341	>	return (s = status) < 0 ? s :
342	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
343	>	(w = (wt = (ForkJoinWorkerThread)t).workQueue).
344	>	tryUnpush(this) && (s = doExec()) < 0 ? s :
345	>	wt.pool.awaitJoin(w, this) :
346	>	externalAwaitDone();
347		}
348
349		/**
350	<	* Sets status to indicate normal completion
350	>	* Implementation for invoke, quietlyInvoke.
351	>	*
352	>	* @return status upon completion
353		*/
354	<	final void setNormalCompletion() {
355	<	// Try typical fast case -- single CAS, no signal, not already done.
356	<	// Manually expand casStatus to improve chances of inlining it
357	<	if (!_unsafe.compareAndSwapInt(this, statusOffset, 0, NORMAL))
358	<	setCompletion(NORMAL);
354	>	private int doInvoke() {
355	>	int s; Thread t; ForkJoinWorkerThread wt;
356	>	return (s = doExec()) < 0 ? s :
357	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
358	>	(wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) :
359	>	externalAwaitDone();
360		}
361
362	<	// internal waiting and notification
362	>	// Exception table support
363
364		/**
365	<	* Performs the actual monitor wait for awaitDone
365	>	* Table of exceptions thrown by tasks, to enable reporting by
366	>	* callers. Because exceptions are rare, we don't directly keep
367	>	* them with task objects, but instead use a weak ref table.  Note
368	>	* that cancellation exceptions don't appear in the table, but are
369	>	* instead recorded as status values.
370	>	*
371	>	* Note: These statics are initialized below in static block.
372		*/
373	<	private void doAwaitDone() {
374	<	// Minimize lock bias and in/de-flation effects by maximizing
375	<	// chances of waiting inside sync
376	<	try {
377	<	while (status >= 0)
378	<	synchronized(this) { if (status >= 0) wait(); }
379	<	} catch (InterruptedException ie) {
380	<	onInterruptedWait();
373	>	private static final ExceptionNode[] exceptionTable;
374	>	private static final ReentrantLock exceptionTableLock;
375	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
376	>
377	>	/**
378	>	* Fixed capacity for exceptionTable.
379	>	*/
380	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
381	>
382	>	/**
383	>	* Key-value nodes for exception table.  The chained hash table
384	>	* uses identity comparisons, full locking, and weak references
385	>	* for keys. The table has a fixed capacity because it only
386	>	* maintains task exceptions long enough for joiners to access
387	>	* them, so should never become very large for sustained
388	>	* periods. However, since we do not know when the last joiner
389	>	* completes, we must use weak references and expunge them. We do
390	>	* so on each operation (hence full locking). Also, some thread in
391	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
392	>	* pool becomes isQuiescent.
393	>	*/
394	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
395	>	final Throwable ex;
396	>	ExceptionNode next;
397	>	final long thrower;  // use id not ref to avoid weak cycles
398	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
399	>	super(task, exceptionTableRefQueue);
400	>	this.ex = ex;
401	>	this.next = next;
402	>	this.thrower = Thread.currentThread().getId();
403		}
404		}
405
406		/**
407	<	* Performs the actual monitor wait for awaitDone
407	>	* Records exception and sets status.
408	>	*
409	>	* @return status on exit
410		*/
411	<	private void doAwaitDone(long startTime, long nanos) {
412	<	synchronized(this) {
411	>	final int recordExceptionalCompletion(Throwable ex) {
412	>	int s;
413	>	if ((s = status) >= 0) {
414	>	int h = System.identityHashCode(this);
415	>	final ReentrantLock lock = exceptionTableLock;
416	>	lock.lock();
417		try {
418	<	while (status >= 0) {
419	<	long nt = nanos - System.nanoTime() - startTime;
420	<	if (nt <= 0)
418	>	expungeStaleExceptions();
419	>	ExceptionNode[] t = exceptionTable;
420	>	int i = h & (t.length - 1);
421	>	for (ExceptionNode e = t[i]; ; e = e.next) {
422	>	if (e == null) {
423	>	t[i] = new ExceptionNode(this, ex, t[i]);
424	>	break;
425	>	}
426	>	if (e.get() == this) // already present
427		break;
237	–	wait(nt / 1000000, (int)(nt % 1000000));
428		}
429	<	} catch (InterruptedException ie) {
430	<	onInterruptedWait();
429	>	} finally {
430	>	lock.unlock();
431		}
432	+	s = setCompletion(EXCEPTIONAL);
433		}
434	+	return s;
435		}
436
437	<	// Awaiting completion
437	>	/**
438	>	* Records exception and possibly propagates.
439	>	*
440	>	* @return status on exit
441	>	*/
442	>	private int setExceptionalCompletion(Throwable ex) {
443	>	int s = recordExceptionalCompletion(ex);
444	>	if ((s & DONE_MASK) == EXCEPTIONAL)
445	>	internalPropagateException(ex);
446	>	return s;
447	>	}
448
449		/**
450	<	* Sets status to indicate there is joiner, then waits for join,
249	<	* surrounded with pool notifications.
250	<	* @return status upon exit
450	>	* Hook for exception propagation support for tasks with completers.
451		*/
452	<	final int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
453	<	ForkJoinPool pool = w == null? null : w.pool;
454	<	int s;
455	<	while ((s = status) >= 0) {
456	<	if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
457	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
458	<	doAwaitDone();
459	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
460	<	adjustPoolCountsOnUnblock(pool);
461	<	break;
452	>	void internalPropagateException(Throwable ex) {
453	>	}
454	>
455	>	/**
456	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
457	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
458	>	* exceptions, but if it does anyway, we have no recourse during
459	>	* shutdown, so guard against this case.
460	>	*/
461	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
462	>	if (t != null && t.status >= 0) {
463	>	try {
464	>	t.cancel(false);
465	>	} catch (Throwable ignore) {
466		}
467		}
264	–	return s;
468		}
469
470		/**
471	<	* Timed version of awaitDone
269	<	* @return status upon exit
471	>	* Removes exception node and clears status
472		*/
473	<	final int awaitDone(ForkJoinWorkerThread w, long nanos) {
474	<	ForkJoinPool pool = w == null? null : w.pool;
475	<	int s;
476	<	while ((s = status) >= 0) {
477	<	if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
478	<	long startTime = System.nanoTime();
479	<	if (pool == null || !pool.preJoin(this, false))
480	<	doAwaitDone(startTime, nanos);
481	<	if ((s = status) >= 0) {
482	<	adjustPoolCountsOnCancelledWait(pool);
483	<	s = status;
473	>	private void clearExceptionalCompletion() {
474	>	int h = System.identityHashCode(this);
475	>	final ReentrantLock lock = exceptionTableLock;
476	>	lock.lock();
477	>	try {
478	>	ExceptionNode[] t = exceptionTable;
479	>	int i = h & (t.length - 1);
480	>	ExceptionNode e = t[i];
481	>	ExceptionNode pred = null;
482	>	while (e != null) {
483	>	ExceptionNode next = e.next;
484	>	if (e.get() == this) {
485	>	if (pred == null)
486	>	t[i] = next;
487	>	else
488	>	pred.next = next;
489	>	break;
490		}
491	<	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
492	<	adjustPoolCountsOnUnblock(pool);
285	<	break;
491	>	pred = e;
492	>	e = next;
493		}
494	+	expungeStaleExceptions();
495	+	status = 0;
496	+	} finally {
497	+	lock.unlock();
498		}
288	–	return s;
499		}
500
501		/**
502	<	* Notify pool that thread is unblocked. Called by signalled
503	<	* threads when woken by non-FJ threads (which is atypical).
502	>	* Returns a rethrowable exception for the given task, if
503	>	* available. To provide accurate stack traces, if the exception
504	>	* was not thrown by the current thread, we try to create a new
505	>	* exception of the same type as the one thrown, but with the
506	>	* recorded exception as its cause. If there is no such
507	>	* constructor, we instead try to use a no-arg constructor,
508	>	* followed by initCause, to the same effect. If none of these
509	>	* apply, or any fail due to other exceptions, we return the
510	>	* recorded exception, which is still correct, although it may
511	>	* contain a misleading stack trace.
512	>	*
513	>	* @return the exception, or null if none
514		*/
515	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
516	<	int s;
517	<	do;while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
518	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
519	<	pool.updateRunningCount(s);
515	>	private Throwable getThrowableException() {
516	>	if ((status & DONE_MASK) != EXCEPTIONAL)
517	>	return null;
518	>	int h = System.identityHashCode(this);
519	>	ExceptionNode e;
520	>	final ReentrantLock lock = exceptionTableLock;
521	>	lock.lock();
522	>	try {
523	>	expungeStaleExceptions();
524	>	ExceptionNode[] t = exceptionTable;
525	>	e = t[h & (t.length - 1)];
526	>	while (e != null && e.get() != this)
527	>	e = e.next;
528	>	} finally {
529	>	lock.unlock();
530	>	}
531	>	Throwable ex;
532	>	if (e == null || (ex = e.ex) == null)
533	>	return null;
534	>	if (false && e.thrower != Thread.currentThread().getId()) {
535	>	Class<? extends Throwable> ec = ex.getClass();
536	>	try {
537	>	Constructor<?> noArgCtor = null;
538	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
539	>	for (int i = 0; i < cs.length; ++i) {
540	>	Constructor<?> c = cs[i];
541	>	Class<?>[] ps = c.getParameterTypes();
542	>	if (ps.length == 0)
543	>	noArgCtor = c;
544	>	else if (ps.length == 1 && ps[0] == Throwable.class)
545	>	return (Throwable)(c.newInstance(ex));
546	>	}
547	>	if (noArgCtor != null) {
548	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
549	>	wx.initCause(ex);
550	>	return wx;
551	>	}
552	>	} catch (Exception ignore) {
553	>	}
554	>	}
555	>	return ex;
556		}
557
558		/**
559	<	* Notify pool to adjust counts on cancelled or timed out wait
559	>	* Poll stale refs and remove them. Call only while holding lock.
560		*/
561	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
562	<	if (pool != null) {
563	<	int s;
564	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
565	<	if (casStatus(s, s - 1)) {
566	<	pool.updateRunningCount(1);
567	<	break;
561	>	private static void expungeStaleExceptions() {
562	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
563	>	if (x instanceof ExceptionNode) {
564	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
565	>	ExceptionNode[] t = exceptionTable;
566	>	int i = System.identityHashCode(key) & (t.length - 1);
567	>	ExceptionNode e = t[i];
568	>	ExceptionNode pred = null;
569	>	while (e != null) {
570	>	ExceptionNode next = e.next;
571	>	if (e == x) {
572	>	if (pred == null)
573	>	t[i] = next;
574	>	else
575	>	pred.next = next;
576	>	break;
577	>	}
578	>	pred = e;
579	>	e = next;
580		}
581		}
582		}
583		}
584
585	<	private void onInterruptedWait() {
586	<	Thread t = Thread.currentThread();
587	<	if (t instanceof ForkJoinWorkerThread) {
588	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)t;
589	<	if (w.isTerminating())
590	<	cancelIgnoreExceptions();
591	<	}
324	<	else { // re-interrupt
585	>	/**
586	>	* If lock is available, poll stale refs and remove them.
587	>	* Called from ForkJoinPool when pools become quiescent.
588	>	*/
589	>	static final void helpExpungeStaleExceptions() {
590	>	final ReentrantLock lock = exceptionTableLock;
591	>	if (lock.tryLock()) {
592		try {
593	<	t.interrupt();
594	<	} catch (SecurityException ignore) {
593	>	expungeStaleExceptions();
594	>	} finally {
595	>	lock.unlock();
596		}
597		}
598		}
599
600	<	// Recording and reporting exceptions
600	>	/**
601	>	* A version of "sneaky throw" to relay exceptions
602	>	*/
603	>	static void rethrow(final Throwable ex) {
604	>	if (ex != null) {
605	>	if (ex instanceof Error)
606	>	throw (Error)ex;
607	>	if (ex instanceof RuntimeException)
608	>	throw (RuntimeException)ex;
609	>	throw uncheckedThrowable(ex, RuntimeException.class);
610	>	}
611	>	}
612
613	<	private void setDoneExceptionally(Throwable rex) {
614	<	exceptionMap.put(this, rex);
615	<	setCompletion(EXCEPTIONAL);
613	>	/**
614	>	* The sneaky part of sneaky throw, relying on generics
615	>	* limitations to evade compiler complaints about rethrowing
616	>	* unchecked exceptions
617	>	*/
618	>	@SuppressWarnings("unchecked") static <T extends Throwable>
619	>	T uncheckedThrowable(final Throwable t, final Class<T> c) {
620	>	return (T)t; // rely on vacuous cast
621		}
622
623		/**
624	<	* Throws the exception associated with status s;
341	<	* @throws the exception
624	>	* Throws exception, if any, associated with the given status.
625		*/
626		private void reportException(int s) {
627	<	if ((s &= COMPLETION_MASK) < NORMAL) {
628	<	if (s == CANCELLED)
629	<	throw new CancellationException();
630	<	else
348	<	rethrowException(exceptionMap.get(this));
349	<	}
627	>	if (s == CANCELLED)
628	>	throw new CancellationException();
629	>	if (s == EXCEPTIONAL)
630	>	rethrow(getThrowableException());
631		}
632
633	+	// public methods
634	+
635		/**
636	<	* Returns result or throws exception using j.u.c.Future conventions
637	<	* Only call when isDone known to be true.
636	>	* Arranges to asynchronously execute this task in the pool the
637	>	* current task is running in, if applicable, or using the {@link
638	>	* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}.  While
639	>	* it is not necessarily enforced, it is a usage error to fork a
640	>	* task more than once unless it has completed and been
641	>	* reinitialized.  Subsequent modifications to the state of this
642	>	* task or any data it operates on are not necessarily
643	>	* consistently observable by any thread other than the one
644	>	* executing it unless preceded by a call to {@link #join} or
645	>	* related methods, or a call to {@link #isDone} returning {@code
646	>	* true}.
647	>	*
648	>	* @return {@code this}, to simplify usage
649		*/
650	<	private V reportFutureResult()
651	<	throws ExecutionException, InterruptedException {
652	<	int s = status & COMPLETION_MASK;
653	<	if (s < NORMAL) {
654	<	Throwable ex;
655	<	if (s == CANCELLED)
656	<	throw new CancellationException();
657	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
658	<	throw new ExecutionException(ex);
659	<	if (Thread.interrupted())
660	<	throw new InterruptedException();
661	<	}
650	>	public final ForkJoinTask<V> fork() {
651	>	Thread t;
652	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
653	>	((ForkJoinWorkerThread)t).workQueue.push(this);
654	>	else
655	>	ForkJoinPool.commonPool.externalPush(this);
656	>	return this;
657	>	}
658	>
659	>	/**
660	>	* Returns the result of the computation when it {@link #isDone is
661	>	* done}.  This method differs from {@link #get()} in that
662	>	* abnormal completion results in {@code RuntimeException} or
663	>	* {@code Error}, not {@code ExecutionException}, and that
664	>	* interrupts of the calling thread do <em>not</em> cause the
665	>	* method to abruptly return by throwing {@code
666	>	* InterruptedException}.
667	>	*
668	>	* @return the computed result
669	>	*/
670	>	public final V join() {
671	>	int s;
672	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
673	>	reportException(s);
674		return getRawResult();
675		}
676
677		/**
678	<	* Returns result or throws exception using j.u.c.Future conventions
679	<	* with timeouts
678	>	* Commences performing this task, awaits its completion if
679	>	* necessary, and returns its result, or throws an (unchecked)
680	>	* {@code RuntimeException} or {@code Error} if the underlying
681	>	* computation did so.
682	>	*
683	>	* @return the computed result
684		*/
685	<	private V reportTimedFutureResult()
686	<	throws InterruptedException, ExecutionException, TimeoutException {
687	<	Throwable ex;
688	<	int s = status & COMPLETION_MASK;
689	<	if (s == NORMAL)
380	<	return getRawResult();
381	<	if (s == CANCELLED)
382	<	throw new CancellationException();
383	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
384	<	throw new ExecutionException(ex);
385	<	if (Thread.interrupted())
386	<	throw new InterruptedException();
387	<	throw new TimeoutException();
685	>	public final V invoke() {
686	>	int s;
687	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
688	>	reportException(s);
689	>	return getRawResult();
690		}
691
692	<	// internal execution methods
692	>	/**
693	>	* Forks the given tasks, returning when {@code isDone} holds for
694	>	* each task or an (unchecked) exception is encountered, in which
695	>	* case the exception is rethrown. If more than one task
696	>	* encounters an exception, then this method throws any one of
697	>	* these exceptions. If any task encounters an exception, the
698	>	* other may be cancelled. However, the execution status of
699	>	* individual tasks is not guaranteed upon exceptional return. The
700	>	* status of each task may be obtained using {@link
701	>	* #getException()} and related methods to check if they have been
702	>	* cancelled, completed normally or exceptionally, or left
703	>	* unprocessed.
704	>	*
705	>	* @param t1 the first task
706	>	* @param t2 the second task
707	>	* @throws NullPointerException if any task is null
708	>	*/
709	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
710	>	int s1, s2;
711	>	t2.fork();
712	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
713	>	t1.reportException(s1);
714	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
715	>	t2.reportException(s2);
716	>	}
717
718		/**
719	<	* Calls exec, recording completion, and rethrowing exception if
720	<	* encountered. Caller should normally check status before calling
721	<	* @return true if completed normally
719	>	* Forks the given tasks, returning when {@code isDone} holds for
720	>	* each task or an (unchecked) exception is encountered, in which
721	>	* case the exception is rethrown. If more than one task
722	>	* encounters an exception, then this method throws any one of
723	>	* these exceptions. If any task encounters an exception, others
724	>	* may be cancelled. However, the execution status of individual
725	>	* tasks is not guaranteed upon exceptional return. The status of
726	>	* each task may be obtained using {@link #getException()} and
727	>	* related methods to check if they have been cancelled, completed
728	>	* normally or exceptionally, or left unprocessed.
729	>	*
730	>	* @param tasks the tasks
731	>	* @throws NullPointerException if any task is null
732		*/
733	<	private boolean tryExec() {
734	<	try { // try block must contain only call to exec
735	<	if (!exec())
736	<	return false;
737	<	} catch (Throwable rex) {
738	<	setDoneExceptionally(rex);
739	<	rethrowException(rex);
740	<	return false; // not reached
733	>	public static void invokeAll(ForkJoinTask<?>... tasks) {
734	>	Throwable ex = null;
735	>	int last = tasks.length - 1;
736	>	for (int i = last; i >= 0; --i) {
737	>	ForkJoinTask<?> t = tasks[i];
738	>	if (t == null) {
739	>	if (ex == null)
740	>	ex = new NullPointerException();
741	>	}
742	>	else if (i != 0)
743	>	t.fork();
744	>	else if (t.doInvoke() < NORMAL && ex == null)
745	>	ex = t.getException();
746		}
747	<	setNormalCompletion();
748	<	return true;
747	>	for (int i = 1; i <= last; ++i) {
748	>	ForkJoinTask<?> t = tasks[i];
749	>	if (t != null) {
750	>	if (ex != null)
751	>	t.cancel(false);
752	>	else if (t.doJoin() < NORMAL)
753	>	ex = t.getException();
754	>	}
755	>	}
756	>	if (ex != null)
757	>	rethrow(ex);
758		}
759
760		/**
761	<	* Main execution method used by worker threads. Invokes
762	<	* base computation unless already complete
761	>	* Forks all tasks in the specified collection, returning when
762	>	* {@code isDone} holds for each task or an (unchecked) exception
763	>	* is encountered, in which case the exception is rethrown. If
764	>	* more than one task encounters an exception, then this method
765	>	* throws any one of these exceptions. If any task encounters an
766	>	* exception, others may be cancelled. However, the execution
767	>	* status of individual tasks is not guaranteed upon exceptional
768	>	* return. The status of each task may be obtained using {@link
769	>	* #getException()} and related methods to check if they have been
770	>	* cancelled, completed normally or exceptionally, or left
771	>	* unprocessed.
772	>	*
773	>	* @param tasks the collection of tasks
774	>	* @return the tasks argument, to simplify usage
775	>	* @throws NullPointerException if tasks or any element are null
776		*/
777	<	final void quietlyExec() {
778	<	if (status >= 0) {
779	<	try {
780	<	if (!exec())
781	<	return;
782	<	} catch(Throwable rex) {
783	<	setDoneExceptionally(rex);
784	<	return;
777	>	public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
778	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
779	>	invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
780	>	return tasks;
781	>	}
782	>	@SuppressWarnings("unchecked")
783	>	List<? extends ForkJoinTask<?>> ts =
784	>	(List<? extends ForkJoinTask<?>>) tasks;
785	>	Throwable ex = null;
786	>	int last = ts.size() - 1;
787	>	for (int i = last; i >= 0; --i) {
788	>	ForkJoinTask<?> t = ts.get(i);
789	>	if (t == null) {
790	>	if (ex == null)
791	>	ex = new NullPointerException();
792		}
793	<	setNormalCompletion();
793	>	else if (i != 0)
794	>	t.fork();
795	>	else if (t.doInvoke() < NORMAL && ex == null)
796	>	ex = t.getException();
797		}
798	+	for (int i = 1; i <= last; ++i) {
799	+	ForkJoinTask<?> t = ts.get(i);
800	+	if (t != null) {
801	+	if (ex != null)
802	+	t.cancel(false);
803	+	else if (t.doJoin() < NORMAL)
804	+	ex = t.getException();
805	+	}
806	+	}
807	+	if (ex != null)
808	+	rethrow(ex);
809	+	return tasks;
810		}
811
812		/**
813	<	* Calls exec, recording but not rethrowing exception
814	<	* Caller should normally check status before calling
815	<	* @return true if completed normally
813	>	* Attempts to cancel execution of this task. This attempt will
814	>	* fail if the task has already completed or could not be
815	>	* cancelled for some other reason. If successful, and this task
816	>	* has not started when {@code cancel} is called, execution of
817	>	* this task is suppressed. After this method returns
818	>	* successfully, unless there is an intervening call to {@link
819	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
820	>	* {@link #isDone}, and {@code cancel} will return {@code true}
821	>	* and calls to {@link #join} and related methods will result in
822	>	* {@code CancellationException}.
823	>	*
824	>	* <p>This method may be overridden in subclasses, but if so, must
825	>	* still ensure that these properties hold. In particular, the
826	>	* {@code cancel} method itself must not throw exceptions.
827	>	*
828	>	* <p>This method is designed to be invoked by <em>other</em>
829	>	* tasks. To terminate the current task, you can just return or
830	>	* throw an unchecked exception from its computation method, or
831	>	* invoke {@link #completeExceptionally}.
832	>	*
833	>	* @param mayInterruptIfRunning this value has no effect in the
834	>	* default implementation because interrupts are not used to
835	>	* control cancellation.
836	>	*
837	>	* @return {@code true} if this task is now cancelled
838		*/
839	<	private boolean tryQuietlyInvoke() {
840	<	try {
841	<	if (!exec())
842	<	return false;
843	<	} catch (Throwable rex) {
844	<	setDoneExceptionally(rex);
845	<	return false;
846	<	}
847	<	setNormalCompletion();
848	<	return true;
839	>	public boolean cancel(boolean mayInterruptIfRunning) {
840	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
841	>	}
842	>
843	>	public final boolean isDone() {
844	>	return status < 0;
845	>	}
846	>
847	>	public final boolean isCancelled() {
848	>	return (status & DONE_MASK) == CANCELLED;
849		}
850
851		/**
852	<	* Cancel, ignoring any exceptions it throws
852	>	* Returns {@code true} if this task threw an exception or was cancelled.
853	>	*
854	>	* @return {@code true} if this task threw an exception or was cancelled
855		*/
856	<	final void cancelIgnoreExceptions() {
857	<	try {
449	<	cancel(false);
450	<	} catch(Throwable ignore) {
451	<	}
856	>	public final boolean isCompletedAbnormally() {
857	>	return status < NORMAL;
858		}
859
860	<	// public methods
860	>	/**
861	>	* Returns {@code true} if this task completed without throwing an
862	>	* exception and was not cancelled.
863	>	*
864	>	* @return {@code true} if this task completed without throwing an
865	>	* exception and was not cancelled
866	>	*/
867	>	public final boolean isCompletedNormally() {
868	>	return (status & DONE_MASK) == NORMAL;
869	>	}
870
871		/**
872	<	* Arranges to asynchronously execute this task.  While it is not
873	<	* necessarily enforced, it is a usage error to fork a task more
874	<	* than once unless it has completed and been reinitialized.  This
875	<	* method may be invoked only from within other ForkJoinTask
876	<	* computations. Attempts to invoke in other contexts result in
877	<	* exceptions or errors including ClassCastException.
878	<	*/
879	<	public final void fork() {
880	<	((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this);
872	>	* Returns the exception thrown by the base computation, or a
873	>	* {@code CancellationException} if cancelled, or {@code null} if
874	>	* none or if the method has not yet completed.
875	>	*
876	>	* @return the exception, or {@code null} if none
877	>	*/
878	>	public final Throwable getException() {
879	>	int s = status & DONE_MASK;
880	>	return ((s >= NORMAL)    ? null :
881	>	(s == CANCELLED) ? new CancellationException() :
882	>	getThrowableException());
883		}
884
885		/**
886	<	* Returns the result of the computation when it is ready.
887	<	* This method differs from <tt>get</tt> in that abnormal
888	<	* completion results in RuntimeExceptions or Errors, not
889	<	* ExecutionExceptions.
886	>	* Completes this task abnormally, and if not already aborted or
887	>	* cancelled, causes it to throw the given exception upon
888	>	* {@code join} and related operations. This method may be used
889	>	* to induce exceptions in asynchronous tasks, or to force
890	>	* completion of tasks that would not otherwise complete.  Its use
891	>	* in other situations is discouraged.  This method is
892	>	* overridable, but overridden versions must invoke {@code super}
893	>	* implementation to maintain guarantees.
894		*
895	<	* @return the computed result
895	>	* @param ex the exception to throw. If this exception is not a
896	>	* {@code RuntimeException} or {@code Error}, the actual exception
897	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
898		*/
899	<	public final V join() {
900	<	ForkJoinWorkerThread w = getWorker();
901	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
902	<	reportException(awaitDone(w, true));
480	<	return getRawResult();
899	>	public void completeExceptionally(Throwable ex) {
900	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
901	>	(ex instanceof Error) ? ex :
902	>	new RuntimeException(ex));
903		}
904
905	<	public final V get() throws InterruptedException, ExecutionException {
906	<	ForkJoinWorkerThread w = getWorker();
907	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
908	<	awaitDone(w, true);
909	<	return reportFutureResult();
905	>	/**
906	>	* Completes this task, and if not already aborted or cancelled,
907	>	* returning the given value as the result of subsequent
908	>	* invocations of {@code join} and related operations. This method
909	>	* may be used to provide results for asynchronous tasks, or to
910	>	* provide alternative handling for tasks that would not otherwise
911	>	* complete normally. Its use in other situations is
912	>	* discouraged. This method is overridable, but overridden
913	>	* versions must invoke {@code super} implementation to maintain
914	>	* guarantees.
915	>	*
916	>	* @param value the result value for this task
917	>	*/
918	>	public void complete(V value) {
919	>	try {
920	>	setRawResult(value);
921	>	} catch (Throwable rex) {
922	>	setExceptionalCompletion(rex);
923	>	return;
924	>	}
925	>	setCompletion(NORMAL);
926		}
927
928	<	public final V get(long timeout, TimeUnit unit)
929	<	throws InterruptedException, ExecutionException, TimeoutException {
930	<	ForkJoinWorkerThread w = getWorker();
931	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
932	<	awaitDone(w, unit.toNanos(timeout));
933	<	return reportTimedFutureResult();
928	>	/**
929	>	* Completes this task normally without setting a value. The most
930	>	* recent value established by {@link #setRawResult} (or {@code
931	>	* null} by default) will be returned as the result of subsequent
932	>	* invocations of {@code join} and related operations.
933	>	*
934	>	* @since 1.8
935	>	*/
936	>	public final void quietlyComplete() {
937	>	setCompletion(NORMAL);
938		}
939
940		/**
941	<	* Possibly executes other tasks until this task is ready, then
942	<	* returns the result of the computation.  This method may be more
943	<	* efficient than <tt>join</tt>, but is only applicable when there
502	<	* are no potemtial dependencies between continuation of the
503	<	* current task and that of any other task that might be executed
504	<	* while helping. (This usually holds for pure divide-and-conquer
505	<	* tasks).
941	>	* Waits if necessary for the computation to complete, and then
942	>	* retrieves its result.
943	>	*
944		* @return the computed result
945	+	* @throws CancellationException if the computation was cancelled
946	+	* @throws ExecutionException if the computation threw an
947	+	* exception
948	+	* @throws InterruptedException if the current thread is not a
949	+	* member of a ForkJoinPool and was interrupted while waiting
950		*/
951	<	public final V helpJoin() {
952	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
953	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
954	<	reportException(w.helpJoinTask(this));
951	>	public final V get() throws InterruptedException, ExecutionException {
952	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
953	>	doJoin() : externalInterruptibleAwaitDone();
954	>	Throwable ex;
955	>	if ((s &= DONE_MASK) == CANCELLED)
956	>	throw new CancellationException();
957	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
958	>	throw new ExecutionException(ex);
959		return getRawResult();
960		}
961
962		/**
963	<	* Performs this task, awaits its completion if necessary, and
964	<	* return its result.
965	<	* @throws Throwable (a RuntimeException, Error, or unchecked
966	<	* exception) if the underlying computation did so.
963	>	* Waits if necessary for at most the given time for the computation
964	>	* to complete, and then retrieves its result, if available.
965	>	*
966	>	* @param timeout the maximum time to wait
967	>	* @param unit the time unit of the timeout argument
968		* @return the computed result
969	+	* @throws CancellationException if the computation was cancelled
970	+	* @throws ExecutionException if the computation threw an
971	+	* exception
972	+	* @throws InterruptedException if the current thread is not a
973	+	* member of a ForkJoinPool and was interrupted while waiting
974	+	* @throws TimeoutException if the wait timed out
975		*/
976	<	public final V invoke() {
977	<	if (status >= 0 && tryExec())
978	<	return getRawResult();
979	<	else
980	<	return join();
976	>	public final V get(long timeout, TimeUnit unit)
977	>	throws InterruptedException, ExecutionException, TimeoutException {
978	>	if (Thread.interrupted())
979	>	throw new InterruptedException();
980	>	// Messy in part because we measure in nanosecs, but wait in millisecs
981	>	int s; long ms;
982	>	long ns = unit.toNanos(timeout);
983	>	if ((s = status) >= 0 && ns > 0L) {
984	>	long deadline = System.nanoTime() + ns;
985	>	ForkJoinPool p = null;
986	>	ForkJoinPool.WorkQueue w = null;
987	>	Thread t = Thread.currentThread();
988	>	if (t instanceof ForkJoinWorkerThread) {
989	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
990	>	p = wt.pool;
991	>	w = wt.workQueue;
992	>	p.helpJoinOnce(w, this); // no retries on failure
993	>	}
994	>	else
995	>	ForkJoinPool.externalHelpJoin(this);
996	>	boolean canBlock = false;
997	>	boolean interrupted = false;
998	>	try {
999	>	while ((s = status) >= 0) {
1000	>	if (w != null && w.qlock < 0)
1001	>	cancelIgnoringExceptions(this);
1002	>	else if (!canBlock) {
1003	>	if (p == null || p.tryCompensate())
1004	>	canBlock = true;
1005	>	}
1006	>	else {
1007	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
1008	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1009	>	synchronized (this) {
1010	>	if (status >= 0) {
1011	>	try {
1012	>	wait(ms);
1013	>	} catch (InterruptedException ie) {
1014	>	if (p == null)
1015	>	interrupted = true;
1016	>	}
1017	>	}
1018	>	else
1019	>	notifyAll();
1020	>	}
1021	>	}
1022	>	if ((s = status) < 0 || interrupted ||
1023	>	(ns = deadline - System.nanoTime()) <= 0L)
1024	>	break;
1025	>	}
1026	>	}
1027	>	} finally {
1028	>	if (p != null && canBlock)
1029	>	p.incrementActiveCount();
1030	>	}
1031	>	if (interrupted)
1032	>	throw new InterruptedException();
1033	>	}
1034	>	if ((s &= DONE_MASK) != NORMAL) {
1035	>	Throwable ex;
1036	>	if (s == CANCELLED)
1037	>	throw new CancellationException();
1038	>	if (s != EXCEPTIONAL)
1039	>	throw new TimeoutException();
1040	>	if ((ex = getThrowableException()) != null)
1041	>	throw new ExecutionException(ex);
1042	>	}
1043	>	return getRawResult();
1044		}
1045
1046		/**
1047	<	* Joins this task, without returning its result or throwing an
1047	>	* Joins this task, without returning its result or throwing its
1048		* exception. This method may be useful when processing
1049		* collections of tasks when some have been cancelled or otherwise
1050		* known to have aborted.
1051		*/
1052		public final void quietlyJoin() {
1053	<	if (status >= 0) {
537	<	ForkJoinWorkerThread w = getWorker();
538	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
539	<	awaitDone(w, true);
540	<	}
1053	>	doJoin();
1054		}
1055
1056		/**
1057	<	* Possibly executes other tasks until this task is ready.
1057	>	* Commences performing this task and awaits its completion if
1058	>	* necessary, without returning its result or throwing its
1059	>	* exception.
1060		*/
1061	<	public final void quietlyHelpJoin() {
1062	<	if (status >= 0) {
548	<	ForkJoinWorkerThread w =
549	<	(ForkJoinWorkerThread)(Thread.currentThread());
550	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
551	<	w.helpJoinTask(this);
552	<	}
1061	>	public final void quietlyInvoke() {
1062	>	doInvoke();
1063		}
1064
1065		/**
1066	<	* Performs this task and awaits its completion if necessary,
1067	<	* without returning its result or throwing an exception. This
1068	<	* method may be useful when processing collections of tasks when
1069	<	* some have been cancelled or otherwise known to have aborted.
1066	>	* Possibly executes tasks until the pool hosting the current task
1067	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
1068	>	* be of use in designs in which many tasks are forked, but none
1069	>	* are explicitly joined, instead executing them until all are
1070	>	* processed.
1071		*/
1072	<	public final void quietlyInvoke() {
1073	<	if (status >= 0 && !tryQuietlyInvoke())
1074	<	quietlyJoin();
1072	>	public static void helpQuiesce() {
1073	>	Thread t;
1074	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
1075	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1076	>	wt.pool.helpQuiescePool(wt.workQueue);
1077	>	}
1078	>	else
1079	>	ForkJoinPool.externalHelpQuiescePool();
1080		}
1081
1082		/**
1083	<	* Returns true if the computation performed by this task has
1084	<	* completed (or has been cancelled).
1085	<	* @return true if this computation has completed
1083	>	* Resets the internal bookkeeping state of this task, allowing a
1084	>	* subsequent {@code fork}. This method allows repeated reuse of
1085	>	* this task, but only if reuse occurs when this task has either
1086	>	* never been forked, or has been forked, then completed and all
1087	>	* outstanding joins of this task have also completed. Effects
1088	>	* under any other usage conditions are not guaranteed.
1089	>	* This method may be useful when executing
1090	>	* pre-constructed trees of subtasks in loops.
1091	>	*
1092	>	* <p>Upon completion of this method, {@code isDone()} reports
1093	>	* {@code false}, and {@code getException()} reports {@code
1094	>	* null}. However, the value returned by {@code getRawResult} is
1095	>	* unaffected. To clear this value, you can invoke {@code
1096	>	* setRawResult(null)}.
1097		*/
1098	<	public final boolean isDone() {
1099	<	return status < 0;
1098	>	public void reinitialize() {
1099	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1100	>	clearExceptionalCompletion();
1101	>	else
1102	>	status = 0;
1103		}
1104
1105		/**
1106	<	* Returns true if this task was cancelled.
1107	<	* @return true if this task was cancelled
1106	>	* Returns the pool hosting the current task execution, or null
1107	>	* if this task is executing outside of any ForkJoinPool.
1108	>	*
1109	>	* @see #inForkJoinPool
1110	>	* @return the pool, or {@code null} if none
1111		*/
1112	<	public final boolean isCancelled() {
1113	<	return (status & COMPLETION_MASK) == CANCELLED;
1112	>	public static ForkJoinPool getPool() {
1113	>	Thread t = Thread.currentThread();
1114	>	return (t instanceof ForkJoinWorkerThread) ?
1115	>	((ForkJoinWorkerThread) t).pool : null;
1116		}
1117
1118		/**
1119	<	* Returns true if this task threw an exception or was cancelled
1120	<	* @return true if this task threw an exception or was cancelled
1119	>	* Returns {@code true} if the current thread is a {@link
1120	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1121	>	*
1122	>	* @return {@code true} if the current thread is a {@link
1123	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1124	>	* or {@code false} otherwise
1125		*/
1126	<	public final boolean completedAbnormally() {
1127	<	return (status & COMPLETION_MASK) < NORMAL;
1126	>	public static boolean inForkJoinPool() {
1127	>	return Thread.currentThread() instanceof ForkJoinWorkerThread;
1128		}
1129
1130		/**
1131	<	* Returns the exception thrown by the base computation, or a
1132	<	* CancellationException if cancelled, or null if none or if the
1133	<	* method has not yet completed.
1134	<	* @return the exception, or null if none
1131	>	* Tries to unschedule this task for execution. This method will
1132	>	* typically (but is not guaranteed to) succeed if this task is
1133	>	* the most recently forked task by the current thread, and has
1134	>	* not commenced executing in another thread.  This method may be
1135	>	* useful when arranging alternative local processing of tasks
1136	>	* that could have been, but were not, stolen.
1137	>	*
1138	>	* @return {@code true} if unforked
1139		*/
1140	<	public final Throwable getException() {
1141	<	int s = status & COMPLETION_MASK;
1142	<	if (s >= NORMAL)
1143	<	return null;
1144	<	if (s == CANCELLED)
602	<	return new CancellationException();
603	<	return exceptionMap.get(this);
1140	>	public boolean tryUnfork() {
1141	>	Thread t;
1142	>	return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1143	>	((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1144	>	ForkJoinPool.tryExternalUnpush(this));
1145		}
1146
1147		/**
1148	<	* Asserts that the results of this task's computation will not be
1149	<	* used. If a cancellation occurs before this task is processed,
1150	<	* then its <tt>compute</tt> method will not be executed,
1151	<	* <tt>isCancelled</tt> will report true, and <tt>join</tt> will
611	<	* result in a CancellationException being thrown. Otherwise, when
612	<	* cancellation races with completion, there are no guarantees
613	<	* about whether <tt>isCancelled</tt> will report true, whether
614	<	* <tt>join</tt> will return normally or via an exception, or
615	<	* whether these behaviors will remain consistent upon repeated
616	<	* invocation.
1148	>	* Returns an estimate of the number of tasks that have been
1149	>	* forked by the current worker thread but not yet executed. This
1150	>	* value may be useful for heuristic decisions about whether to
1151	>	* fork other tasks.
1152		*
1153	<	* <p>This method may be overridden in subclasses, but if so, must
1154	<	* still ensure that these minimal properties hold. In particular,
1155	<	* the cancel method itself must not throw exceptions.
1153	>	* @return the number of tasks
1154	>	*/
1155	>	public static int getQueuedTaskCount() {
1156	>	Thread t; ForkJoinPool.WorkQueue q;
1157	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1158	>	q = ((ForkJoinWorkerThread)t).workQueue;
1159	>	else
1160	>	q = ForkJoinPool.commonSubmitterQueue();
1161	>	return (q == null) ? 0 : q.queueSize();
1162	>	}
1163	>
1164	>	/**
1165	>	* Returns an estimate of how many more locally queued tasks are
1166	>	* held by the current worker thread than there are other worker
1167	>	* threads that might steal them, or zero if this thread is not
1168	>	* operating in a ForkJoinPool. This value may be useful for
1169	>	* heuristic decisions about whether to fork other tasks. In many
1170	>	* usages of ForkJoinTasks, at steady state, each worker should
1171	>	* aim to maintain a small constant surplus (for example, 3) of
1172	>	* tasks, and to process computations locally if this threshold is
1173	>	* exceeded.
1174		*
1175	<	* <p> This method is designed to be invoked by <em>other</em>
1176	<	* tasks. To terminate the current task, you can just return or
1177	<	* throw an unchecked exception from its computation method, or
1178	<	* invoke <tt>completeExceptionally(someException)</tt>.
1175	>	* @return the surplus number of tasks, which may be negative
1176	>	*/
1177	>	public static int getSurplusQueuedTaskCount() {
1178	>	return ForkJoinPool.getSurplusQueuedTaskCount();
1179	>	}
1180	>
1181	>	// Extension methods
1182	>
1183	>	/**
1184	>	* Returns the result that would be returned by {@link #join}, even
1185	>	* if this task completed abnormally, or {@code null} if this task
1186	>	* is not known to have been completed.  This method is designed
1187	>	* to aid debugging, as well as to support extensions. Its use in
1188	>	* any other context is discouraged.
1189		*
1190	<	* @param mayInterruptIfRunning this value is ignored in the
1191	<	* default implementation because tasks are not in general
1192	<	* cancelled via interruption.
1190	>	* @return the result, or {@code null} if not completed
1191	>	*/
1192	>	public abstract V getRawResult();
1193	>
1194	>	/**
1195	>	* Forces the given value to be returned as a result.  This method
1196	>	* is designed to support extensions, and should not in general be
1197	>	* called otherwise.
1198		*
1199	<	* @return true if this task is now cancelled
1199	>	* @param value the value
1200		*/
1201	<	public boolean cancel(boolean mayInterruptIfRunning) {
634	<	setCompletion(CANCELLED);
635	<	return (status & COMPLETION_MASK) == CANCELLED;
636	<	}
1201	>	protected abstract void setRawResult(V value);
1202
1203		/**
1204	<	* Completes this task abnormally, and if not already aborted or
1205	<	* cancelled, causes it to throw the given exception upon
1206	<	* <tt>join</tt> and related operations. This method may be used
1207	<	* to induce exceptions in asynchronous tasks, or to force
1208	<	* completion of tasks that would not otherwise complete.  This
1209	<	* method is overridable, but overridden versions must invoke
1210	<	* <tt>super</tt> implementation to maintain guarantees.
1211	<	* @param ex the exception to throw. If this exception is
1212	<	* not a RuntimeException or Error, the actual exception thrown
1213	<	* will be a RuntimeException with cause ex.
1204	>	* Immediately performs the base action of this task and returns
1205	>	* true if, upon return from this method, this task is guaranteed
1206	>	* to have completed normally. This method may return false
1207	>	* otherwise, to indicate that this task is not necessarily
1208	>	* complete (or is not known to be complete), for example in
1209	>	* asynchronous actions that require explicit invocations of
1210	>	* completion methods. This method may also throw an (unchecked)
1211	>	* exception to indicate abnormal exit. This method is designed to
1212	>	* support extensions, and should not in general be called
1213	>	* otherwise.
1214	>	*
1215	>	* @return {@code true} if this task is known to have completed normally
1216		*/
1217	<	public void completeExceptionally(Throwable ex) {
651	<	setDoneExceptionally((ex instanceof RuntimeException) ||
652	<	(ex instanceof Error)? ex :
653	<	new RuntimeException(ex));
654	<	}
1217	>	protected abstract boolean exec();
1218
1219		/**
1220	<	* Completes this task, and if not already aborted or cancelled,
1221	<	* returning a <tt>null</tt> result upon <tt>join</tt> and related
1222	<	* operations. This method may be used to provide results for
1223	<	* asynchronous tasks, or to provide alternative handling for
1224	<	* tasks that would not otherwise complete normally.
1220	>	* Returns, but does not unschedule or execute, a task queued by
1221	>	* the current thread but not yet executed, if one is immediately
1222	>	* available. There is no guarantee that this task will actually
1223	>	* be polled or executed next. Conversely, this method may return
1224	>	* null even if a task exists but cannot be accessed without
1225	>	* contention with other threads.  This method is designed
1226	>	* primarily to support extensions, and is unlikely to be useful
1227	>	* otherwise.
1228		*
1229	<	* @param value the result value for this task.
1229	>	* @return the next task, or {@code null} if none are available
1230		*/
1231	<	public void complete(V value) {
1232	<	try {
1233	<	setRawResult(value);
1234	<	} catch(Throwable rex) {
1235	<	setDoneExceptionally(rex);
1236	<	return;
1237	<	}
672	<	setNormalCompletion();
1231	>	protected static ForkJoinTask<?> peekNextLocalTask() {
1232	>	Thread t; ForkJoinPool.WorkQueue q;
1233	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1234	>	q = ((ForkJoinWorkerThread)t).workQueue;
1235	>	else
1236	>	q = ForkJoinPool.commonSubmitterQueue();
1237	>	return (q == null) ? null : q.peek();
1238		}
1239
1240		/**
1241	<	* Resets the internal bookkeeping state of this task, allowing a
1242	<	* subsequent <tt>fork</tt>. This method allows repeated reuse of
1243	<	* this task, but only if reuse occurs when this task has either
1244	<	* never been forked, or has been forked, then completed and all
1245	<	* outstanding joins of this task have also completed. Effects
1246	<	* under any other usage conditions are not guaranteed, and are
1247	<	* almost surely wrong. This method may be useful when executing
683	<	* pre-constructed trees of subtasks in loops.
1241	>	* Unschedules and returns, without executing, the next task
1242	>	* queued by the current thread but not yet executed, if the
1243	>	* current thread is operating in a ForkJoinPool.  This method is
1244	>	* designed primarily to support extensions, and is unlikely to be
1245	>	* useful otherwise.
1246	>	*
1247	>	* @return the next task, or {@code null} if none are available
1248		*/
1249	<	public void reinitialize() {
1250	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
1251	<	exceptionMap.remove(this);
1252	<	status = 0;
1249	>	protected static ForkJoinTask<?> pollNextLocalTask() {
1250	>	Thread t;
1251	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1252	>	((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
1253	>	null;
1254		}
1255
1256		/**
1257	<	* Tries to unschedule this task for execution. This method will
1258	<	* typically succeed if this task is the next task that would be
1259	<	* executed by the current thread, and will typically fail (return
1260	<	* false) otherwise. This method may be useful when arranging
1261	<	* faster local processing of tasks that could have been, but were
1262	<	* not, stolen.
1263	<	* @return true if unforked
1257	>	* If the current thread is operating in a ForkJoinPool,
1258	>	* unschedules and returns, without executing, the next task
1259	>	* queued by the current thread but not yet executed, if one is
1260	>	* available, or if not available, a task that was forked by some
1261	>	* other thread, if available. Availability may be transient, so a
1262	>	* {@code null} result does not necessarily imply quiescence of
1263	>	* the pool this task is operating in.  This method is designed
1264	>	* primarily to support extensions, and is unlikely to be useful
1265	>	* otherwise.
1266	>	*
1267	>	* @return a task, or {@code null} if none are available
1268		*/
1269	<	public boolean tryUnfork() {
1270	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this);
1269	>	protected static ForkJoinTask<?> pollTask() {
1270	>	Thread t; ForkJoinWorkerThread wt;
1271	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1272	>	(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
1273	>	null;
1274		}
1275
1276	+	// tag operations
1277	+
1278		/**
1279	<	* Forks both tasks, returning when <tt>isDone</tt> holds for both
1280	<	* of them or an exception is encountered. This method may be
1281	<	* invoked only from within other ForkJoinTask
1282	<	* computations. Attempts to invoke in other contexts result in
709	<	* exceptions or errors including ClassCastException.
710	<	* @param t1 one task
711	<	* @param t2 the other task
712	<	* @throws NullPointerException if t1 or t2 are null
713	<	* @throws RuntimeException or Error if either task did so.
1279	>	* Returns the tag for this task.
1280	>	*
1281	>	* @return the tag for this task
1282	>	* @since 1.8
1283		*/
1284	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
1285	<	t2.fork();
717	<	t1.invoke();
718	<	t2.join();
1284	>	public final short getForkJoinTaskTag() {
1285	>	return (short)status;
1286		}
1287
1288		/**
1289	<	* Forks the given tasks, returning when <tt>isDone</tt> holds for
1290	<	* all of them. If any task encounters an exception, others may be
1291	<	* cancelled.  This method may be invoked only from within other
1292	<	* ForkJoinTask computations. Attempts to invoke in other contexts
1293	<	* result in exceptions or errors including ClassCastException.
727	<	* @param tasks the array of tasks
728	<	* @throws NullPointerException if tasks or any element are null.
729	<	* @throws RuntimeException or Error if any task did so.
1289	>	* Atomically sets the tag value for this task.
1290	>	*
1291	>	* @param tag the tag value
1292	>	* @return the previous value of the tag
1293	>	* @since 1.8
1294		*/
1295	<	public static void invokeAll(ForkJoinTask<?>... tasks) {
1296	<	Throwable ex = null;
1297	<	int last = tasks.length - 1;
1298	<	for (int i = last; i >= 0; --i) {
1299	<	ForkJoinTask<?> t = tasks[i];
736	<	if (t == null) {
737	<	if (ex == null)
738	<	ex = new NullPointerException();
739	<	}
740	<	else if (i != 0)
741	<	t.fork();
742	<	else {
743	<	t.quietlyInvoke();
744	<	if (ex == null)
745	<	ex = t.getException();
746	<	}
1295	>	public final short setForkJoinTaskTag(short tag) {
1296	>	for (int s;;) {
1297	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1298	>	(s & ~SMASK) | (tag & SMASK)))
1299	>	return (short)s;
1300		}
1301	<	for (int i = 1; i <= last; ++i) {
1302	<	ForkJoinTask<?> t = tasks[i];
1303	<	if (t != null) {
1304	<	if (ex != null)
1305	<	t.cancel(false);
1306	<	else {
1307	<	t.quietlyJoin();
1308	<	if (ex == null)
1309	<	ex = t.getException();
1310	<	}
1311	<	}
1301	>	}
1302	>
1303	>	/**
1304	>	* Atomically conditionally sets the tag value for this task.
1305	>	* Among other applications, tags can be used as visit markers
1306	>	* in tasks operating on graphs, as in methods that check: {@code
1307	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1308	>	* before processing, otherwise exiting because the node has
1309	>	* already been visited.
1310	>	*
1311	>	* @param e the expected tag value
1312	>	* @param tag the new tag value
1313	>	* @return true if successful; i.e., the current value was
1314	>	* equal to e and is now tag.
1315	>	* @since 1.8
1316	>	*/
1317	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1318	>	for (int s;;) {
1319	>	if ((short)(s = status) != e)
1320	>	return false;
1321	>	if (U.compareAndSwapInt(this, STATUS, s,
1322	>	(s & ~SMASK) | (tag & SMASK)))
1323	>	return true;
1324		}
760	–	if (ex != null)
761	–	rethrowException(ex);
1325		}
1326
1327		/**
1328	<	* Forks all tasks in the collection, returning when
1329	<	* <tt>isDone</tt> holds for all of them. If any task encounters
1330	<	* an exception, others may be cancelled.  This method may be
768	<	* invoked only from within other ForkJoinTask
769	<	* computations. Attempts to invoke in other contexts result in
770	<	* exceptions or errors including ClassCastException.
771	<	* @param tasks the collection of tasks
772	<	* @throws NullPointerException if tasks or any element are null.
773	<	* @throws RuntimeException or Error if any task did so.
1328	>	* Adaptor for Runnables. This implements RunnableFuture
1329	>	* to be compliant with AbstractExecutorService constraints
1330	>	* when used in ForkJoinPool.
1331		*/
1332	<	public static void invokeAll(Collection<? extends ForkJoinTask<?>> tasks) {
1333	<	if (!(tasks instanceof List)) {
1334	<	invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
1335	<	return;
1332	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1333	>	implements RunnableFuture<T> {
1334	>	final Runnable runnable;
1335	>	T result;
1336	>	AdaptedRunnable(Runnable runnable, T result) {
1337	>	if (runnable == null) throw new NullPointerException();
1338	>	this.runnable = runnable;
1339	>	this.result = result; // OK to set this even before completion
1340		}
1341	<	List<? extends ForkJoinTask<?>> ts =
1342	<	(List<? extends ForkJoinTask<?>>)tasks;
1343	<	Throwable ex = null;
1344	<	int last = ts.size() - 1;
1345	<	for (int i = last; i >= 0; --i) {
785	<	ForkJoinTask<?> t = ts.get(i);
786	<	if (t == null) {
787	<	if (ex == null)
788	<	ex = new NullPointerException();
789	<	}
790	<	else if (i != 0)
791	<	t.fork();
792	<	else {
793	<	t.quietlyInvoke();
794	<	if (ex == null)
795	<	ex = t.getException();
796	<	}
797	<	}
798	<	for (int i = 1; i <= last; ++i) {
799	<	ForkJoinTask<?> t = ts.get(i);
800	<	if (t != null) {
801	<	if (ex != null)
802	<	t.cancel(false);
803	<	else {
804	<	t.quietlyJoin();
805	<	if (ex == null)
806	<	ex = t.getException();
807	<	}
808	<	}
809	<	}
810	<	if (ex != null)
811	<	rethrowException(ex);
1341	>	public final T getRawResult() { return result; }
1342	>	public final void setRawResult(T v) { result = v; }
1343	>	public final boolean exec() { runnable.run(); return true; }
1344	>	public final void run() { invoke(); }
1345	>	private static final long serialVersionUID = 5232453952276885070L;
1346		}
1347
1348		/**
1349	<	* Possibly executes tasks until the pool hosting the current task
816	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
817	<	* designs in which many tasks are forked, but none are explicitly
818	<	* joined, instead executing them until all are processed.
1349	>	* Adaptor for Runnables without results
1350		*/
1351	<	public static void helpQuiesce() {
1352	<	((ForkJoinWorkerThread)(Thread.currentThread())).
1353	<	helpQuiescePool();
1351	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1352	>	implements RunnableFuture<Void> {
1353	>	final Runnable runnable;
1354	>	AdaptedRunnableAction(Runnable runnable) {
1355	>	if (runnable == null) throw new NullPointerException();
1356	>	this.runnable = runnable;
1357	>	}
1358	>	public final Void getRawResult() { return null; }
1359	>	public final void setRawResult(Void v) { }
1360	>	public final boolean exec() { runnable.run(); return true; }
1361	>	public final void run() { invoke(); }
1362	>	private static final long serialVersionUID = 5232453952276885070L;
1363		}
1364
1365		/**
1366	<	* Returns a estimate of how many more locally queued tasks are
827	<	* held by the current worker thread than there are other worker
828	<	* threads that might want to steal them.  This value may be
829	<	* useful for heuristic decisions about whether to fork other
830	<	* tasks. In many usages of ForkJoinTasks, at steady state, each
831	<	* worker should aim to maintain a small constant surplus (for
832	<	* example, 3) of tasks, and to process computations locally if
833	<	* this threshold is exceeded.
834	<	* @return the surplus number of tasks, which may be negative
1366	>	* Adaptor for Callables
1367		*/
1368	<	public static int surplus() {
1369	<	return ((ForkJoinWorkerThread)(Thread.currentThread()))
1370	<	.getEstimatedSurplusTaskCount();
1368	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1369	>	implements RunnableFuture<T> {
1370	>	final Callable<? extends T> callable;
1371	>	T result;
1372	>	AdaptedCallable(Callable<? extends T> callable) {
1373	>	if (callable == null) throw new NullPointerException();
1374	>	this.callable = callable;
1375	>	}
1376	>	public final T getRawResult() { return result; }
1377	>	public final void setRawResult(T v) { result = v; }
1378	>	public final boolean exec() {
1379	>	try {
1380	>	result = callable.call();
1381	>	return true;
1382	>	} catch (Error err) {
1383	>	throw err;
1384	>	} catch (RuntimeException rex) {
1385	>	throw rex;
1386	>	} catch (Exception ex) {
1387	>	throw new RuntimeException(ex);
1388	>	}
1389	>	}
1390	>	public final void run() { invoke(); }
1391	>	private static final long serialVersionUID = 2838392045355241008L;
1392		}
1393
841	–	// Extension kit
842	–
1394		/**
1395	<	* Returns the result that would be returned by <tt>join</tt>, or
1396	<	* null if this task is not known to have been completed.  This
1397	<	* method is designed to aid debugging, as well as to support
847	<	* extensions. Its use in any other context is discouraged.
1395	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1396	>	* method of the given {@code Runnable} as its action, and returns
1397	>	* a null result upon {@link #join}.
1398		*
1399	<	* @return the result, or null if not completed.
1399	>	* @param runnable the runnable action
1400	>	* @return the task
1401		*/
1402	<	public abstract V getRawResult();
1402	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1403	>	return new AdaptedRunnableAction(runnable);
1404	>	}
1405
1406		/**
1407	<	* Forces the given value to be returned as a result.  This method
1408	<	* is designed to support extensions, and should not in general be
1409	<	* called otherwise.
1407	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1408	>	* method of the given {@code Runnable} as its action, and returns
1409	>	* the given result upon {@link #join}.
1410		*
1411	<	* @param value the value
1411	>	* @param runnable the runnable action
1412	>	* @param result the result upon completion
1413	>	* @return the task
1414		*/
1415	<	protected abstract void setRawResult(V value);
1415	>	public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1416	>	return new AdaptedRunnable<T>(runnable, result);
1417	>	}
1418
1419		/**
1420	<	* Immediately performs the base action of this task.  This method
1421	<	* is designed to support extensions, and should not in general be
1422	<	* called otherwise. The return value controls whether this task
1423	<	* is considered to be done normally. It may return false in
1424	<	* asynchronous actions that require explicit invocations of
1425	<	* <tt>complete</tt> to become joinable. It may throw exceptions
1426	<	* to indicate abnormal exit.
870	<	* @return true if completed normally
871	<	* @throws Error or RuntimeException if encountered during computation
1420	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1421	>	* method of the given {@code Callable} as its action, and returns
1422	>	* its result upon {@link #join}, translating any checked exceptions
1423	>	* encountered into {@code RuntimeException}.
1424	>	*
1425	>	* @param callable the callable action
1426	>	* @return the task
1427		*/
1428	<	protected abstract boolean exec();
1428	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1429	>	return new AdaptedCallable<T>(callable);
1430	>	}
1431
1432		// Serialization support
1433
1434		private static final long serialVersionUID = -7721805057305804111L;
1435
1436		/**
1437	<	* Save the state to a stream.
1437	>	* Saves this task to a stream (that is, serializes it).
1438		*
1439		* @serialData the current run status and the exception thrown
1440	<	* during execution, or null if none.
884	<	* @param s the stream
1440	>	* during execution, or {@code null} if none
1441		*/
1442		private void writeObject(java.io.ObjectOutputStream s)
1443		throws java.io.IOException {
#	Line 890 | Line 1446 | public abstract class ForkJoinTask<V> im
1446		}
1447
1448		/**
1449	<	* Reconstitute the instance from a stream.
894	<	* @param s the stream
1449	>	* Reconstitutes this task from a stream (that is, deserializes it).
1450		*/
1451		private void readObject(java.io.ObjectInputStream s)
1452		throws java.io.IOException, ClassNotFoundException {
1453		s.defaultReadObject();
899	–	//        status &= ~INTERNAL_SIGNAL_MASK; //  todo: define policy
1454		Object ex = s.readObject();
1455		if (ex != null)
1456	<	setDoneExceptionally((Throwable)ex);
1456	>	setExceptionalCompletion((Throwable)ex);
1457		}
1458
1459	<	// Temporary Unsafe mechanics for preliminary release
1460	<
1461	<	static final Unsafe _unsafe;
908	<	static final long statusOffset;
1459	>	// Unsafe mechanics
1460	>	private static final sun.misc.Unsafe U;
1461	>	private static final long STATUS;
1462
1463		static {
1464	+	exceptionTableLock = new ReentrantLock();
1465	+	exceptionTableRefQueue = new ReferenceQueue<Object>();
1466	+	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1467		try {
1468	<	if (ForkJoinTask.class.getClassLoader() != null) {
1469	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1470	<	f.setAccessible(true);
1471	<	_unsafe = (Unsafe)f.get(null);
1472	<	}
1473	<	else
1474	<	_unsafe = Unsafe.getUnsafe();
919	<	statusOffset = _unsafe.objectFieldOffset
920	<	(ForkJoinTask.class.getDeclaredField("status"));
921	<	} catch (Exception ex) { throw new Error(ex); }
1468	>	U = getUnsafe();
1469	>	Class<?> k = ForkJoinTask.class;
1470	>	STATUS = U.objectFieldOffset
1471	>	(k.getDeclaredField("status"));
1472	>	} catch (Exception e) {
1473	>	throw new Error(e);
1474	>	}
1475		}
1476
1477	+	/**
1478	+	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1479	+	* Replace with a simple call to Unsafe.getUnsafe when integrating
1480	+	* into a jdk.
1481	+	*
1482	+	* @return a sun.misc.Unsafe
1483	+	*/
1484	+	private static sun.misc.Unsafe getUnsafe() {
1485	+	try {
1486	+	return sun.misc.Unsafe.getUnsafe();
1487	+	} catch (SecurityException se) {
1488	+	try {
1489	+	return java.security.AccessController.doPrivileged
1490	+	(new java.security
1491	+	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1492	+	public sun.misc.Unsafe run() throws Exception {
1493	+	java.lang.reflect.Field f = sun.misc
1494	+	.Unsafe.class.getDeclaredField("theUnsafe");
1495	+	f.setAccessible(true);
1496	+	return (sun.misc.Unsafe) f.get(null);
1497	+	}});
1498	+	} catch (java.security.PrivilegedActionException e) {
1499	+	throw new RuntimeException("Could not initialize intrinsics",
1500	+	e.getCause());
1501	+	}
1502	+	}
1503	+	}
1504		}

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